This invention relates to a composition and process for disposing of radioactive, hazardous and mixed wastes, and, in particular, to encapsulation and stabilization of low-level radioactive, hazardous and mixed wastes.
Industrial wastes which are not economical to recycle must be disposed of in the environment. Some of this waste material can be rendered harmless and then disposed of in a convenient manner. Other wastes, however, such as heavy metals, for example, mercury, lead, antimony, arsenic, and radioactive substances, cannot be rendered harmless. Consequently, the disposal of these materials into the environment must be made in a manner in which they are stabilized against dispersion into the environment.
Large volumes of low-level radioactive wastes are routinely generated through the operation of defense-related and commercial nuclear facilities. As a result of its defense and research activities, the Department of Energy (DOE) generates not only low level radioactive waste, but also hazardous and mixed waste. Hazardous and mixed wastes at DOE facilities include a broad range of waste types, such as evaporator concentrates, salts, blowdown slurries, sludges, filter materials, ion exchange resins, and incinerator ash, that encompass diverse physical and chemical properties. Many of these wastes have been identified as problem wastes because they are difficult to encapsulate using conventional technologies and/or produce waste forms of poor quality that do not successfully retain hazardous constituents in the disposal environment.
Due to reductions in volume resulting from incineration of contaminated combustible materials, remaining ash residues may contain sufficient quantities of hazardous elements, including heavy metals, that they meet the Environment Protection Agency (EPA) definitions for hazardous waste as well as DOE definitions for low-level radioactive waste. According to EPA's guidelines for delisting of hazardous and mixed wastes, before disposal at approved low-level waste disposal sites, such wastes must first be treated to immobilize the hazardous constituents.
Attempts have been made in the past to render radioactive, hazardous and mixed wastes harmless by immobilizing the wastes against dispersion by ecological forces.
In one method, the mixed wastes are sealed into metal or plastic containers which are then stored underground or in the ocean. In another method, the wastes are incorporated into a matrix of materials, such as inorganic cements and polymers while in their fluid or molten state followed by solidification. The high viscosity of molten plastics generally has limited the quantity of waste which can be loaded into the plastic matrix.
Frequently, incorporation of wastes in a plastic mixture is limited by the inability of the matrix to isolate the waste from the environment. Highly loaded matrices having over 30 percent loadings have been unsatisfactory because of leaching. Thus, one disadvantage of known processes used to encapsulate waste is the tendency of waste to become mobilized. Other disadvantages of conventional hydraulic cement and other thermosetting polymer processes include low efficiency of waste encapsulation, a requirement to cure the matrix by adding chemicals and/or increasing the temperature, steps which result in increased operating costs.
Accordingly, there is still a need in the art of waste disposal to provide a composition and method for encapsulating and stabilizing radioactive, hazardous and mixed wastes.
It is, therefore, an object of the present invention to provide a composition and process for encapsulating and stabilizing radioactive, hazardous and mixed wastes in a multi-barrier process. Another object of this invention is to provide durable waste forms which can withstand mobilization by ecological forces. Yet, another object of the present invention is to develop an encapsulating process which has no curing requirements for solidification, thus providing significant cost savings.